Confinement or movement of an object using  focused ultrasound waves to generate anultrasound intensity well

ABSTRACT

A method includes transmitting a focused ultrasound wave into a medium to form (i) an ultrasound intensity well within the medium that exhibits a first range of acoustic pressure and (ii) a surrounding region of the medium that surrounds the ultrasound intensity well and exhibits a second range of acoustic pressure that exceeds the first range of acoustic pressure. The method further includes confining an object within the ultrasound intensity well. Additionally, an acoustic lens is configured to be acoustically coupled to an acoustic transducer. The acoustic lens has a varying longitudinal thickness that increases proportionally with respect to increasing azimuth angle of the acoustic lens. Another acoustic lens is configured to be acoustically coupled to an acoustic that increases proportionally with respect to increasing azimuth angle of the segment.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 62/046,654, filed on Sep. 5, 2014, the contents of whichare incorporated herein by reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Grant Nos. 1R01DK092197-02, 2P01 DK043881-15, 2R01 EB007643-05, and 2T32 DK007779-11A1,awarded by the National Institutes of Health. The government has certainrights in the invention.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Previously known methods using ultrasound waves to acoustically confineor move an object are ineffective in moving or confining some objects.For instance, these methods are not well suited for moving or confininga large object, an object with a high mass density, or an object throughwhich acoustic waves travel at a high rate of speed, such as a kidneystone.

SUMMARY

An example method includes transmitting a focused ultrasound wave into amedium to form (i) an ultrasound intensity well within the medium thatexhibits a first range of acoustic pressure and (ii) a surroundingregion of the medium that surrounds the ultrasound intensity well andexhibits a second range of acoustic pressure that exceeds the firstrange of acoustic pressure. The method further includes confining anobject within the ultrasound intensity well.

An example acoustic lens is configured to be acoustically coupled to anacoustic transducer. The acoustic lens has a varying longitudinalthickness that increases proportionally with respect to increasingazimuth angle of the acoustic lens.

Another example acoustic lens is configured to be acoustically coupledto an acoustic transducer. The acoustic lens includes a plurality ofsegments. Each of the plurality of segments has a varying longitudinalthickness that increases proportionally with respect to increasingazimuth angle of the segment.

An example device includes an acoustic transducer, one or moreprocessors, and a computer-readable medium. The computer-readable mediumstores instructions that, when executed by the one or more processors,cause the acoustic transducer to perform functions. The functionsinclude transmitting a focused ultrasound wave into a medium to form (i)an ultrasound intensity well within the medium that exhibits a firstrange of acoustic pressure and (ii) a surrounding region of the mediumthat surrounds the ultrasound intensity well and exhibits a second rangeof acoustic pressure that exceeds the first range of acoustic pressure.The functions further include confining an object within the ultrasoundintensity well.

An example computer-readable medium stores instructions that, whenexecuted by a computing device comprising an acoustic transducer and/oran acoustic lens, cause the acoustic transducer and/or the acoustic lensto perform functions. The functions include transmitting a focusedultrasound wave into a medium to form (i) an ultrasound intensity wellwithin the medium that exhibits a first range of acoustic pressure and(ii) a surrounding region of the medium that surrounds the ultrasoundintensity well and exhibits a second range of acoustic pressure thatexceeds the first range of acoustic pressure. The functions furtherinclude confining an object within the ultrasound intensity well.

When the term “substantially” or “about” is used herein, it is meantthat the recited characteristic, parameter, or value need not beachieved exactly, but that deviations or variations, including forexample, tolerances, measurement error, measurement accuracy limitationsand other factors known to those of skill in the art, may occur inamounts that do not preclude the effect the characteristic was intendedto provide. In some examples disclosed herein. “substantially” or“about” means within +/−5% of the recited value.

As used herein, the term “ultrasound” may generally refer to frequenciesof acoustic waves that are higher than the range of frequenciestypically perceptible by humans (e.g., 20 Hz-20 kHz), but this termshould not be interpreted as excluding embodiments that include acousticwaves with frequencies that fall within the range of frequenciestypically perceptible by humans.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of an example acoustic transducerdevice.

FIG. 2 shows an example acoustic transducer.

FIG. 3 shows an example acoustic lens configured for phase-shifting andfocusing of components of an ultrasound wave.

FIG. 4 shows another example acoustic lens configured for phase-shiftingand focusing of components of an ultrasound wave.

FIG. 5 is a block diagram depicting an example method for confining ormoving an object using an ultrasound wave.

FIG. 6 shows an example ultrasound wave.

FIGS. 7A, 7B, 7C, 7D, and 7E show measured pressure amplitudes within afocal plane of a medium for various values of L.

FIG. 8 shows the effect of an example acoustic lens upon measuredpressure amplitudes within a focal plane of a medium.

FIGS. 9A, 9B, 9C, and 9D show confinement or movement of an object usingan ultrasound wave.

FIG. 10 shows rotation of an example object via a mechanical torqueprovided by an ultrasound wave.

DETAILED DESCRIPTION

As noted above, previously known methods using ultrasound waves to moveor confine objects are ineffective for objects of large size or highmass density. The methods and systems disclosed herein are suitable formoving or confining objects that are larger and/or denser than theobjects that can be confined or moved using previously known methods.For example, an acoustic transducer may transmit a focused ultrasoundwave into a medium to form (i) an ultrasound intensity well within themedium that exhibits a first range of acoustic pressure and (ii) asurrounding region of the medium that surrounds the ultrasound intensitywell and exhibits a second range of acoustic pressure that exceeds thefirst range of acoustic pressure. In some examples, the ultrasoundintensity well may take on a somewhat circular shape that is defined bythe surrounding region of the medium. By forming the ultrasoundintensity well around an object or by steering a pre-formed ultrasoundintensity well so as to surround the object, the object may be confinedwithin the ultrasound intensity well. The ultrasound intensity well mayalso be steered (mechanically and/or electronically) to move the objectwithin the medium. More specifically, the object may be moved indirections transverse to the propagation direction of the ultrasoundwave.

In one example, a progressive phase shift is imparted to the ultrasoundwave via the acoustic transducer. The acoustic transducer may include m(piezoelectric) transducer elements arranged in a circular pattern. Eachof the m transducer elements may transmit a respective component of theultrasound wave that is phase shifted by 2πL/m radians with respect to acomponent of the ultrasound wave transmitted by an adjacent transducerelement. L may be a nonzero integer and m may be greater than or equalto 3, for example. Input signals representing the various phase-shiftedcomponents of the ultrasound wave may be provided to the respectivetransducer elements via a signal generator, for example. In this way,the progressive phase shift is imparted to the ultrasound wave withrespect to an azimuth angle of the acoustic transducer from which thevarious components of the acoustic wave are transmitted, resulting inthe formation of the ultrasound intensity well. The diameter of theultrasound intensity well may be increased by (electronically)increasing the magnitude of L and decreased by (electronically)decreasing the magnitude of L.

In another example, the progressive phase shift is imparted to theultrasound wave via a first acoustic lens. The first acoustic lens mayhave a varying longitudinal thickness that increases proportionally withrespect to increasing azimuth angle of the first acoustic lens. Forinstance, a single-phase acoustic transducer may transmit a firstcomponent of the ultrasound wave through the first acoustic lens at afirst azimuth angle θ=θ₁ and the first acoustic lens may impart a firstphase shift L*θ₁ to the first component. L may be a nonzero integerdefined by the varying longitudinal thickness of the first acousticlens. The acoustic transducer may also transmit a second component ofthe ultrasound wave through the first acoustic lens at a second azimuthangle θ=θ₂ and the first acoustic lens may impart a second phase shiftL*θ₂ to the second component. In this way, a progressive phase shift isimparted to the ultrasound wave with respect to an azimuth angle of theacoustic transducer from which the various components of the acousticwave are transmitted, resulting in the formation of the ultrasoundintensity well. The diameter of the ultrasound intensity well may beincreased by increasing the magnitude of L (e.g., by increasing thethickness of the first acoustic lens) and decreased by decreasing themagnitude of L (e.g., by decreasing the thickness of the first acousticlens). In some examples, the first acoustic lens may also include anadditional section with a curved surface configured to focus the variouscomponents of the ultrasound wave into a focal plane of the medium.

In another example, the progressive phase shift is imparted to theultrasound wave via a second acoustic lens comprising p segments. Eachof the p segments may have a varying longitudinal thickness thatincreases proportionally with respect to increasing azimuth angle of thesegment. A single-phase acoustic transducer may transmit a firstcomponent of the ultrasound wave through the second acoustic lens at afirst azimuth angle θ=θ₃. The second acoustic lens may impart a firstphase shift L*θ₃ to the first component. L may be an integer multiple ofp. The acoustic transducer may also transmit a second component of theultrasound wave through the second acoustic lens at a second azimuthangle θ=θ₄. The second acoustic lens may impart a second phase shiftL*θ₄ to the second component. In this way, a progressive phase shift isimparted to the ultrasound wave with respect to an azimuth angle of theacoustic transducer from which the various components of the acousticwave are transmitted, resulting in the formation of the ultrasoundintensity well. The diameter of the ultrasound intensity well may beincreased by increasing the magnitude of L (e.g., increasing p, thenumber of segments of the second acoustic lens) and decreased bydecreasing the magnitude of L (e.g., decreasing p). In some examples,the second acoustic lens may also include a second section with a curvedsurface configured to focus the various components of the ultrasoundwave into the medium.

Referring now to the Figures. FIG. 1 illustrates an example acoustictransducer device 100 configured to move or confine an object 122 withina medium 116 by transmitting a focused ultrasound wave 114 into themedium 116. The device 100 may include a processor 102, data storage104, an input/output interface 106, a sensor module 108, and an acoustictransducer 110, any or all of which may be communicatively coupled toeach other via a system bus or another connection mechanism 111. In someexamples, the device 100 may also include an acoustic lens 112 that isacoustically coupled to the acoustic transducer 110.

The processor 102 may include a general purpose processor and/or aspecial purpose processor configured to execute program instructionsstored within data storage 104. In some examples, the processor 102 maybe a multi-core processor comprised of one or more processing unitsconfigured to coordinate to execute instructions stored within datastorage 104. In one example, by executing program instructions storedwithin data storage 104, the processor 102 may provide input signals orsignal parameters to the acoustic transducer 110 for transmission,steering, and/or focusing of the ultrasound wave 114. In anotherexample, the processor 102 may provide to the acoustic transducer 110,input signals or signal parameters based on input received via theinput/output interface 106.

Data storage 104 may include one or more volatile, non-volatile,removable, and/or non-removable storage components. Data storage 104 maybe a magnetic, optical, or flash storage medium, and may be integratedin whole or in part with the processor 102 or other portions of thedevice 100. Further, the data storage 104 may be a non-transitorycomputer-readable storage medium, having stored thereon programinstructions that, when executed by the processor 102, cause the device100 to perform any function described in this disclosure. Such programinstructions may be part of a software application that can be executedin response to inputs received from the input/output interface 106, forinstance. The data storage 104 may also store other types of informationor data, such as those types described throughout this disclosure.

The input/output interface 106 may enable interaction with a user of thedevice 100, if applicable. The input/output interface 106 may includeinput components such as dials, buttons, a keyboard, a mouse, a keypad,or a touch-sensitive panel, and output components such as a displayscreen (which, for example, may be combined with a touch-sensitivepanel), a sound speaker, and a haptic feedback system. In one example,the input/output interface 106 may receive input indicating (i) variousparameters defining the ultrasound wave 114 and/or (ii) variousparameters for steering or focusing the ultrasound wave 114 upon variousportions of the medium 116.

In some examples, the input/output interface 106 may include a displayscreen for displaying images of the object 122 or other sensory datacollected by the sensor module 108. Properly positioning the ultrasoundwave 114 upon or near the object 122 will generally involvecharacterizing the size, shape, location, and/or consistency of theobject 122. The display screen may display images of the object 122 thatare captured by the sensor module 108. The displayed images of theobject 122 may be used prior to transmission of the ultrasound wave 114,or could be used in a real-time manner by monitoring the position of theobject 122 while the ultrasound wave 114 is being transmitted.

The sensor module 108 may include any known hardware and/or softwareconfigured to collect sensory data from the object 122 or the medium 116prior to, during, or after transmission of the ultrasound wave 114. Forexample, the sensor module 108 may include an imaging system to capturean image of the object 122 and provide the captured image to theinput/output interface 106 for display. The sensor module 108 mayinclude an (additional) acoustic transducer configured to (i) generateultrasound waves that are scattered and/or reflected by the object 122,(ii) detect the ultrasound waves reflected and/or scattered by theobject 122, and (iii) generate an image of the object 122 using thedetected ultrasound waves. In another example, the sensor module 108 mayinclude a magnetic resonance imaging (MRI) system. Any known imagingtechnique capable of imaging an object located within a human subject orvarious other media 116 is contemplated herein.

In some examples, the sensor module 108 may be integrated with theacoustic transducer 110. For instance, a single acoustic transducer ortransducer array may be used for both moving/confining the object 122and for imaging of the object 122.

The acoustic transducer 110 may include a signal generator configured toreceive data or signals from the processor 102 or input/output interface106 that is representative of parameters for the ultrasound wave 114.For instance, the processor 102 may send, to the acoustic transducer110, data representative of input received via the input/outputinterface 106. In another example, the received input may simplyindicate one of several predetermined ultrasound wave transmissionprotocols represented by program instructions stored at data storage104. Such data received by the acoustic transducer 110 may indicatevarious ultrasound parameters such as operating power of the acoustictransducer 110, power density of the ultrasound wave 114, oscillationfrequency of the ultrasound wave 114, pulse duration of the ultrasoundwave 114, duty cycle of the ultrasound wave 114, and a number ofultrasound pulses to be generated, for example. The received data mayalso indicate a trajectory, path, or sequence of locations of the medium116 along which the object 122 is to be moved. In other examples, thepath of the ultrasound wave 114 may be manually and/or mechanicallydirected. In some examples, the acoustic transducer 110 may include asignal amplifier used to generate the ultrasound wave 114 at a desiredpower.

The acoustic transducer 110 may include one or more piezoelectrictransducer elements configured to transmit components of the ultrasoundwave 114 in response to receiving respective input signals representingthe components of the ultrasound wave 114. For example, the acoustictransducer 110 may include a phased array of transducer elementsconfigured to electronically focus or steer the ultrasound wave 114 uponvarious portions of the medium 116 and/or the object 122. Eachtransducer element of the acoustic transducer 110 may receive its ownindependent input signal or data. The acoustic transducer 110 may alsoinclude one or more transducer elements having a radius of curvaturecorresponding to a focal plane of the ultrasound wave 114/medium 116.The acoustic transducer 110 may be configured to generate an ultrasoundwave of oscillation frequency ranging from 20 kHz-10 MHz, but otherexamples are possible.

In another example, the acoustic transducer 110 includes only a singletransducer element or is provided with only a single-phase input signal.Here, the acoustic transducer 110 may be acoustically coupled to theacoustic lens 112 to generate the ultrasound wave 114 having theprogressive phase shift.

In some examples, the acoustic lens 112 may impart varying degrees ofphase shift to various components of the ultrasound wave 114 based onthe region through which the various components pass through theacoustic lens 112. The acoustic lens 112 may include any material thatdiffers in sound speed from the medium 116. That is, acoustic waves(e.g., sound/ultrasound waves) may propagate at different respectivespeeds through the acoustic lens 112 and the medium 116. The acousticlens 112 may be made of materials such as plastics, ceramics, and/ormetals. In one example, the acoustic lens 112 includes a UV-curedphotopolymer plastic Accura 60. The acoustic lens 112 may include othermaterials as well. Example acoustic lenses 300 and 400 are depictedrespectively in FIGS. 3 and 4 and discussed in more detail below.

The medium 116 may include any medium that surrounds, contains, orcontacts the object 122, such as intact tissue of a living humansubject, dissected biological tissue, a liquid medium (e.g., water), amedium (e.g., agar) on a petri dish, a liquid medium on a microscopeslide, or the like. Further examples of the medium 116 may include aurinary tract, a renal tract, a ureter, a bladder, a urethra, a prostategland, a salivary gland, a gall bladder, a gall tract, a blood vessel,or an intestinal tract. In some examples, the medium 116 may surround orcontact a portion of the acoustic lens 112 and be acoustically coupledto the acoustic lens 112. In other examples, the medium 116 may bedirectly acoustically coupled to the acoustic transducer 110.

The object 122 may include any object suitable for movement and/orconfinement via interaction with the ultrasound wave 114. Some examplesof the object 122 include: a kidney stone, a urinary tract stone, aureter stone, a bladder stone, a urethra stone, a prostate stone, asalivary stone, a gallbladder stone, a gall stone, a bile duct, a bloodclot, blood, mucous, fecal matter, cerumen, a calcification, a calcifiedplaque, an atherosclerotic plaque, uric acid, struvite, calcium oxalatemonohydrate, cysteine, a tonsil stone, solid non-biological matter, anelectronic component, biological tissue, or non-biological tissue.

The ultrasound intensity well 118 is formed by transmission of theultrasound wave 114 into the medium 116. The ultrasound intensity well118 represents a region of the medium 116 which exhibits a first rangeof acoustic pressure.

The surrounding region 120 represents a region of the medium 116 thatsurrounds the ultrasound intensity well 118 and which exhibits a secondrange of acoustic pressure that exceeds the first range of acousticpressure. The absolute pressure values of the first and second ranges ofpressure are not important.

FIG. 2 is a detailed view of an acoustic transducer 210, includingtransducer elements 213A, 213B, 213C, 213D, 213E, 213F, 213G, 213H,213I, 213J, 213K, and 213L. In some examples, the transducer elements213A-L may be arranged and shaped (e.g., curved) so as to transmit anultrasound wave that is focused at an axial distance of 75 mm from acenter of the acoustic transducer 110. The acoustic transducer 110 mayhave (i) a central opening having a diameter of approximately 11 mm and(ii) an outer diameter of approximately 75 mm.

As described above with regard to FIG. 1, each of the transducerelements 213A-L may be configured to receive an independent input signalfrom a signal generator of the acoustic transducer 110, from theprocessor 102, or from the input/output interface 106. Each of thetransducer elements 213A-L may be configured to vibrate at a frequencyand a phase represented by the respective input signals received, thustransmitting the ultrasound wave 114.

In another example (not shown), the acoustic transducer 110 may includeonly a single-element transducer configured to transmit a single-phaseultrasound wave 114. In some cases, the single-element transducer may becurved so as to focus the ultrasound wave 114 upon a focal plane of themedium 116 that surrounds or contacts the object 122. In the case of thesingle-element transducer, it may be beneficial to acoustically couplethe acoustic transducer 110 to an acoustic lens 300 or 400 of FIGS. 3and 4 respectively, so that an azimuthally-dependent progressive phaseshift may be imparted to the ultrasound wave 114 via the acoustic lens300 or 400.

FIG. 3 shows an example acoustic lens 300 configured for phase-shiftingand/or focusing of components 314A and 314B of an ultrasound wave (e.g.,ultrasound wave 114). In various embodiments, the acoustic lens 300 mayinclude one or both of the first section 312A and the second section312B. In a first embodiment of the acoustic lens 300, only the firstsection 312A is acoustically coupled to the acoustic transducer 110. Ina second embodiment of the acoustic lens 300, only the second section312B is acoustically coupled to the acoustic transducer 110. In a thirdembodiment of the acoustic lens 300, the first section 312A isacoustically coupled to the acoustic transducer 110 and the secondsection 312B is acoustically coupled to the first section 312A. In afourth embodiment of the acoustic lens 300, the second section 312B isacoustically coupled to the acoustic transducer 110 and the firstsection 312A is acoustically coupled to the second section 312B.

The first section 312A may have a varying longitudinal thickness (e.g.,a thickness parallel to the propagation direction of components 314A and314B). The varying longitudinal thickness may increase proportionallywith respect to increasing azimuth angle of the acoustic lens 300. Forexample, the first section 312A may have a first longitudinal thicknessA*L*θ₁+B at a first azimuth angle θ=θ₁, and a second longitudinalthickness A*L*θ₂+B at a second azimuth angle θ=θ₂. The first section312A may also include a boundary at which the varying longitudinalthickness of the first section 312A discontinuously changes fromA*L*2π+B to B.

A and B may be nonzero positive numbers and L may be a nonzero integer.B may correspond to a minimum longitudinal thickness of the firstsection 312A at θ=0 (i.e., θ=2π). The value of L may correspond to arange of phase shifts that the first section 312A may impart to variouscomponents of an ultrasound wave that pass through the first section312A. In some examples, L is equal to −6, −5, −4, −3, −2, −1, 1, 2, 3,4, 5, or 6, corresponding to progressive phase shifts of −12π, −10π,−8π, −6π, −4π, −2π, 2π, 4π, 6π, 8π, 10π, and 12π across a full θ=2πsweep of the azimuth angle. The value of L may determine a diameter ofthe ultrasound intensity well 118. That is, the diameter of theultrasound intensity well 118 may be proportional to the magnitude of L.Additionally, A may be defined by the equation

$\begin{matrix}{A = \frac{\lambda_{m}}{2\; {\pi \left( {1 - n} \right)}}} & \lbrack 1\rbrack\end{matrix}$

where λ_(m) is greater than about 148.2 μm and less than about 74.1 mm(roughly corresponding to wavelengths of acoustic waves of frequencyranging from about 20 kHz to 10 MHz traveling through a water medium).More specifically, λ_(m) may be about equal to 988 μm (roughlycorresponding to a wavelength of an acoustic wave of frequency of about1.5 MHz traveling through a water medium). In another example, λ_(m) maybe about equal to 4.49 mm (roughly corresponding to a wavelength of anacoustic wave of frequency of about 0.33 MHz traveling through a watermedium). n may be an acoustic refractive index of the acoustic lens 300relative to the medium 116. For example, if n=3, then acoustic waveswould travel three times slower through the acoustic lens 300 thanthrough the medium 116. In another example, if n=0.5, then acousticwaves would travel two times faster through the acoustic lens 300 thanthrough the medium 116.

As shown in FIG. 3, a longitudinal thickness of the first section 312Amay be substantially constant along a radial direction of the firstsection 312A of the acoustic lens 300.

The second section 312B may include a curved surface 316 configured tofocus, upon a focal plane of the medium 116, components of an ultrasoundwave received at respective azimuth angles of the acoustic lens 300.

Additional functional applications of the acoustic lens 300 will bediscussed further below.

FIG. 4 shows an example acoustic lens 400 configured for phase-shiftingand focusing of components 414A and 414B of an ultrasound wave (e.g.,ultrasound wave 114). In various embodiments, the acoustic lens 400 mayinclude one or both of the first section 412A and the second section412B. In a first embodiment of the acoustic lens 400, only the firstsection 412A is acoustically coupled to the acoustic transducer 110. Ina second embodiment of the acoustic lens 400, only the second section412B is acoustically coupled to the acoustic transducer 110. In a thirdembodiment of the acoustic lens 400, the first section 412A isacoustically coupled to the acoustic transducer 110 and the secondsection 412B is acoustically coupled to the first section 412A. In afourth embodiment of the acoustic lens 400, the second section 412B isacoustically coupled to the acoustic transducer 110 and the firstsection 412A is acoustically coupled to the second section 412B.

The first section 412A may include a plurality of segments 413A, 413B,413C, 413D, 413E, and 413F. Each of the plurality of segments 413A-F mayhave a varying longitudinal thickness that increases proportionally withrespect to increasing azimuth angle of the segment. For example, thesegment 413D may have a first longitudinal thickness C*L*θ₃+D at a firstazimuth angle θ=θ₃, and a second longitudinal thickness C*L*θ₄+D at asecond azimuth angle θ=θ₄. The first section 412A may include a boundarybetween the segment 413D and the segment 413C at which a longitudinalthickness of the first section 412A changes from C*L*(π/3)+D to D (forthe case where L=6). In the case of a generalized first section 412Ahaving p segments, the first section 412A may include a boundary betweenadjacent segments at which a longitudinal thickness of the first section412A changes from C*L*(2π/p)+D to D.

C and D may be nonzero positive numbers and L may be an integer multipleof p (an integer multiple of 6 in the case of the first section 412A). Dmay correspond to a minimum longitudinal thickness of the segment 413Dat θ=0. In some examples, L is equal to −6, −5, −4, −3, −2, 2, 3, 4, 5,or 6. In the example depicted in FIG. 4, p is equal to 6, so L may beequal to integer multiples of 6, respectively corresponding to phaseshift ranges of (+/−)2π, (+/−)4π, (+/−)6π, etc. across a full π/3 sweepof an azimuth angle of the segment 413D. In the generalized case of psegments, a total range of phase shift imparted to the ultrasound waveby a given segment may be equal to 2πL/p. In some examples, L may beequal to the number of segments of the first section 412A (e.g. L=p=6).The value of L may determine a diameter of the ultrasound intensity well118. That is, the diameter of the ultrasound intensity well 118 may beproportional to the magnitude of L. Additionally, C may be defined bythe equation

$\begin{matrix}{C = \frac{\lambda_{m}}{2\; {\pi \left( {1 - n} \right)}}} & \lbrack 2\rbrack\end{matrix}$

where λ_(m) is greater than about 148.2 μm and less than about 74.1 mm(roughly corresponding to wavelengths of acoustic waves of frequencyranging from about 20 kHz to 10 MHz traveling through a water medium).More specifically, λ_(m) may be about equal to 988 μm (roughlycorresponding to a wavelength of an acoustic wave of frequency of about1.5 MHz traveling through a water medium). In another example, λ_(m) maybe about equal to 4.49 mm (roughly corresponding to a wavelength of anacoustic wave of frequency of about 0.33 MHz traveling through a watermedium). n may be an acoustic refractive index of the acoustic lens 400relative to the medium 116. For example, if n=3, then acoustic waveswould travel three times slower through the acoustic lens 400 thanthrough the medium 116. In another example, if n=0.5, then acousticwaves would travel two times faster through the acoustic lens 400 thanthrough the medium 116.

As shown in FIG. 4, a longitudinal thickness of the first section 412Amay be substantially constant along a radial direction of the firstsection 412A.

The second section 412B may include a curved surface 416 configured tofocus, upon a focal plane of the medium 116, components of an ultrasoundwave received at respective azimuth angles of the acoustic lens 400.

Additional functional applications of the acoustic lens 400 will bediscussed further below.

FIG. 5 is a flow chart depicting an example method 500 for confining ormoving an object using an ultrasound wave. Method 500 shown in FIG. 5presents an example method that can be implemented within an operatingenvironment including, for example, the acoustic transducer device 100,the acoustic transducer 110, the acoustic lens 112, the medium 116, theobject 122, the acoustic lens 300, and the acoustic lens 400. Method 500may include one or more operations, functions, or actions as illustratedby one or more of blocks 502 and 504. Although the blocks areillustrated in sequential order, these blocks may also be performed inparallel, and/or in a different order than those described herein. Also,the various blocks may be combined into fewer blocks, divided intoadditional blocks, and/or removed based upon the desired implementation.

In addition, for the methods 500 and other processes and methodsdisclosed herein, the flowcharts show functionality and operation of onepossible implementation of present embodiments. In this regard, eachblock may represent a module, a segment, or a portion of program code,which includes one or more instructions executable by a processor forimplementing specific logical functions or steps in the process. Theprogram code may be stored on any type of computer-readable medium, forexample, such as a storage device including a disk(s) or hard drive(s).In some embodiments, the program code may be stored in memory (e.g.,disks or disk arrays) associated with and/or connected to a serversystem that makes the program code available for download todesktop/laptop computers, smart phones, tablet computers, or other typesof computing devices. The computer-readable medium may includenon-transitory computer-readable media, for example, such ascomputer-readable media that stores data for short periods of time likeregister memory, processor cache, and Random Access Memory (RAM). Thecomputer-readable medium may also include non-transitory media, such assecondary or persistent long-term storage, like read-only memory (ROM),optical or magnetic disks, compact-disc read-only memory (CD-ROM), forexample. The computer-readable media may also be any other volatile ornon-volatile storage systems. The computer-readable medium may beconsidered a computer-readable storage medium, for example, or atangible storage device. In addition, for the method 500 and otherprocesses and methods disclosed herein, each block in FIG. 5 mayrepresent circuitry that is wired to perform the specific logicalfunctions in the process.

At block 502, the method 500 includes transmitting a focused ultrasoundwave into a medium to form (i) an ultrasound intensity well within themedium that exhibits a first range of acoustic pressure and (ii) asurrounding region of the medium that surrounds the ultrasound intensitywell and exhibits a second range of acoustic pressure that exceeds thefirst range of acoustic pressure.

As shown in FIG. 1, the acoustic transducer 110 may transmit theultrasound wave 114 into the medium 116 to form the ultrasound intensitywell 118 within the medium 116. In order to transmit the ultrasound wave114, the acoustic transducer 110 may receive an input voltage rangingfrom 90-100 V and a time-averaged power of 2.25 W, but other examplesare possible. The ultrasound intensity well 118 may exhibit a firstrange of acoustic pressure (discussed in more detail below). Theultrasound wave 114 may also form the surrounding region 120 within themedium 116 that exhibits a second range of acoustic pressure thatexceeds the first range of acoustic pressure (discussed in more detailbelow).

FIG. 6 shows an example ultrasound wave 114 transmitted by the acoustictransducer 110. The ultrasound wave 114 may have an oscillationfrequency f_(osc) ranging from 20 kHz to 10 MHz (e.g., 1.5 MHz or 0.33MHz). The ultrasound wave 114 may have a pulse repetition frequency f₂of about 100 Hz and a pulse duration t₁ of about 33.3 μs. Other examplesare possible as well.

Transmitting the ultrasound wave may include each transducer element ofan array of m transducer elements transmitting a respective component ofthe ultrasound wave that is phase shifted by 2πL/m radians with respectto a component of the ultrasound wave transmitted by an adjacenttransducer element. L may be any nonzero integer (e.g., −6, −5, −4, −3,−2, −1, 1, 2, 3, 4, 5, or 6) and m may be greater than or equal to 3(e.g., m=12). Other examples are possible.

For instance, the transducer elements 213A-L may each transmit acomponent of the ultrasound wave 114 with respective phase shiftsaccording to the table below.

Transducer Element Phase Shift 213A 0 213B  πL/6 213C  πL/3 213D  πL/2213E 2πL/3 213F 5πL/6 213G πL  213H 7πL/6 213I 4πL/3 213J 3πL/2 213K5πL/3 213L 11πL/6 Transmitting the ultrasound wave 114 with such varying degrees of phaseshift may form the ultrasound intensity well 118 and the surroundingregion 120.

In another example, an acoustic transducer 110 may transmit a firstcomponent 314A and a second component 314B of the ultrasound wave 114.In this example, the first component 314A and the second component 314B(as transmitted by the acoustic transducer 110) might have no phaseshift relative to each other. The acoustic transducer 110 may transmitthe first component 314A through the first section 312A at a firstazimuth angle θ=θ₁. The first section 312A may impart a first phaseshift L*θ₁ to the first component 314A. L may be any nonzero integer(e.g., −6, −5, −4, −3, −2, −1, 1, 2, 3, 4, 5, or 6). The acoustictransducer 110 may also transmit the second component 314B through thefirst section 312A at a second azimuth angle θ=θ₂. The first section312A may impart a second phase shift L*θ₂ to the second component 314B.

At the first azimuth angle θ=θ₁, the first section 312A may have a firstlongitudinal thickness A*L*θ₁+B, and at the second azimuth angle θ=θ₂the first section 312A may have a second longitudinal thicknessA*L*θ₂+B. A may be defined by

$\begin{matrix}{A = \frac{1}{2\; {\pi \left( {\frac{1}{\lambda_{m}} - \frac{1}{\lambda_{p}}} \right)}}} & \lbrack 3\rbrack\end{matrix}$

where λ_(m) is a wavelength of the ultrasound wave 114 propagatingthrough the medium 116, and λ_(p) is a wavelength of the ultrasound wave114 propagating through the acoustic lens 300.

After the first component 314A passes through the first section 312A,the first component 314A may be transmitted through the second section312B. A curved surface 316 of the second section 312B may focus thefirst component 314A upon a focal plane of the medium 116.

After the second component 314B passes through the first section 312A,the second component 314B may be transmitted through the second section312B. The curved surface 316 of the second section 312B may focus thesecond component 314B upon the focal plane of the medium 116.

In other examples, the acoustic lens 300 may be configured such that thecomponents 314A and 314B of the ultrasound wave 114 may first passthrough the second section 312B to be focused and then pass through thefirst section 312A to have the respective phase shifts applied.

FIGS. 7A-F show measured pressure amplitudes within a focal plane of amedium 716 for various values of L. FIG. 7A shows an ultrasoundintensity well 718A surrounded by a surrounding region 720A formed by anultrasound wave corresponding to L=1. As shown, the diameter of theultrasound intensity well 718A was on the order of a few tenths of amillimeter and the diameter of the surrounding region 720A wasapproximately 2.25 mm. The ultrasound intensity well 718A exhibited afirst range of acoustic pressure of approximately 0-0.3 MPa and thesurrounding region 720A exhibited a second range of acoustic pressure ofapproximately 0.3-0.7 MPa.

FIG. 7B shows an ultrasound intensity well 718B surrounded by asurrounding region 720B of a medium 716 formed by an ultrasound wavecorresponding to L=3. As shown, the diameter of the ultrasound intensitywell 718B was about 2 mm and the diameter of the surrounding region 720Bwas approximately 4.5 mm. The ultrasound intensity well 718B exhibited afirst range of acoustic pressure of approximately 0-0.3 MPa and thesurrounding region 720B exhibited a second range of acoustic pressure ofapproximately 0.3-0.4 MPa.

FIG. 7C shows an ultrasound intensity well 718C surrounded by asurrounding region 720C of a medium 716 formed by an ultrasound wavecorresponding to L=4. As shown, the diameter of the ultrasound intensitywell 718C was about 2.25 mm and the diameter of the surrounding region720C was approximately 5.5 mm. The ultrasound intensity well 718Cexhibited a first range of acoustic pressure of approximately 0-0.15 MPaand the surrounding region 720C exhibited a second range of acousticpressure of approximately 0.15-0.35 MPa.

FIG. 7D shows an ultrasound intensity well 718D surrounded by asurrounding region 720D of a medium 716 formed by an ultrasound wavecorresponding to L=5. As shown, the diameter of the ultrasound intensitywell 718D was about 3.25 mm and the diameter of the surrounding region720D was approximately 8.5 mm. The ultrasound intensity well 718Dexhibited a first range of acoustic pressure of approximately 0-0.2 MPaand the surrounding region 720D exhibited a second range of acousticpressure of approximately 0.2-0.4 MPa.

FIG. 7E shows an ultrasound intensity well 718E surrounded by asurrounding region 720E of a medium 716 formed by an ultrasound wavecorresponding to L=6. As shown, the diameter of the ultrasound intensitywell 718E was about 3.5 mm and the diameter of the surrounding region720E was approximately 8.5 mm. The ultrasound intensity well 718Eexhibited a first range of acoustic pressure of approximately 0-0.2 MPaand the surrounding region 720E exhibited a second range of acousticpressure of approximately 0.2-0.4 MPa.

In another example, transmitting the ultrasound wave into the medium mayinclude transmitting a first component of the ultrasound wave through anacoustic lens comprising p segments, where p is greater than or equal to2. The first component may be transmitted through the acoustic lens at afirst azimuth angle θ=θ₃ and the acoustic lens may impart a first phaseshift L*θ₃ to the first component. L may be an integer multiple of p (orperhaps equal to p). Transmitting the ultrasound wave into the mediummay also include transmitting a second component of the ultrasound wavethrough the acoustic lens at a second azimuth angle θ=θ₄. The acousticlens may impart a second phase shift L*θ₄ to the second component.

Referring to FIG. 4 for example, the acoustic transducer 110 maytransmit a first component 414A of the ultrasound wave 114 through thesegment 413D of the first section 412A at a first azimuth angle θ=θ₃.The first section 412A may impart a first phase shift L*θ₃ to the firstcomponent 414A. L may be an integer multiple of p, or in some cases Lmay be equal to p. L may take on values such as −6, −5, −4, −3, −2, −1,1, 2, 3, 4, 5, or 6. In the example depicted in FIG. 4, p=6(corresponding to segments 413A-F). The acoustic transducer 110 may alsotransmit a second component 414B of the ultrasound wave 114 through thesegment 413D of the first section 412A at a second azimuth angle θ=θ₄.The first section 412A may impart a second phase shift L*θ₄ to thesecond component 414B.

After the first component 414A passes through the first section 412A,the first component 414A may be transmitted through the second section412B. A curved surface 416 of the second section 412B may focus thefirst component 414A upon a focal plane of the medium 116.

After the second component 414B passes through the first section 412A,the second component 414B may be transmitted through the second section412B. The curved surface 416 of the second section 412B may focus thesecond component 414B upon the focal plane of the medium 116.

In other examples, the acoustic lens 400 may be configured such that thecomponents 414A and 414B of the ultrasound wave 114 may first passthrough the second section 412B to be focused and then pass through thefirst section 412A to have the respective phase shifts applied.

At the first azimuth angle θ=θ₃ the first section 412A may have a firstlongitudinal thickness C*L*θ₃+D, where C and D are nonzero positivenumbers. At the second azimuth angle θ=θ₄ the first section 412A mayhave a second longitudinal thickness C*L*θ₄+D. C may be defined by

$\begin{matrix}{C = \frac{1}{2\; {\pi \left( {\frac{1}{\lambda_{m}} - \frac{1}{\lambda_{p}}} \right)}}} & \lbrack 4\rbrack\end{matrix}$

where λ_(m) is a wavelength of the ultrasound wave 114 propagatingthrough the medium 116, and λ_(p) is a wavelength of the ultrasound wave114 propagating through the acoustic lens 400.

Regardless of whether the ultrasound wave 114 is focused using theacoustic transducer 210 or using the acoustic lens 300 or 400, theultrasound wave 114 may be focused at a focal plane of the medium 116.This may result in the formation of the ultrasound intensity well 118within the focal plane and a surrounding region 120 that has an annularshape within the focal plane. The ultrasound wave 114 may be focusedupon a focal point (e.g., a center point) within the ultrasoundintensity well 118. The focal point may exhibit a local minimum ofacoustic pressure within the focal plane.

FIG. 8 shows the effect of an example acoustic lens 400 upon measuredpressure amplitude within a focal plane of a medium 116. FIG. 8 shows anultrasound intensity well 818 surrounded by a surrounding region 820 ofa medium 816 formed by an ultrasound wave. As shown, the diameter of theultrasound intensity well 818 was about 7 mm and the diameter of thesurrounding region 820 was approximately 13 mm. The ultrasound intensitywell 818 exhibited a first range of acoustic pressure of approximately0-0.035 MPa and the surrounding region 820 exhibited a second range ofacoustic pressure of approximately 0.035-0.06 MPa.

At block 504, the method 500 includes confining an object within theultrasound intensity well. As shown in FIG. 9A, an ultrasound intensitywell 118 and a surrounding region 120 is formed within the medium 116via transmission of an ultrasound wave by an acoustic transducer. In theexample of FIG. 9A, the ultrasound intensity well 118 and thesurrounding region 120 are formed away from the location of the object122 within the medium 116.

In FIG. 9B, the ultrasound intensity well 118 and the surrounding region120 has been electronically or mechanically steered so that theultrasound intensity well 118 surrounds the object 122. In anotherexample, FIG. 9B depicts formation of the ultrasound intensity well 118and the surrounding region 120 around the object 122, instead offormation of the ultrasound intensity well 118 and the surroundingregion 120 away from the object 122 followed by steering of theultrasound intensity well 118 and the surrounding region 120 toward theobject 122.

When compared to FIG. 9B, in FIG. 9C the ultrasound intensity well 118and the surrounding region 120 have been steered downward, moving theobject 122 downward as well. The downward direction depicted in FIGS. 9Band 9C may be normal to the direction of propagation of the ultrasoundwave 114. That is, steering of the ultrasound wave 114 may causemovement of the object 122 in directions substantially parallel to thefocal plane of the medium 116 (i.e., directions normal to the directionof propagation of the ultrasound wave 114).

When compared to FIG. 9C, in FIG. 9D the ultrasound intensity well 118and the surrounding region 120 have been steered leftward, moving theobject 122 leftward as well. The leftward direction depicted in FIGS. 8Cand 8D may be normal to the direction of propagation of the ultrasoundwave 114.

As mentioned previously, the ultrasound wave 114 may be focused at afocal plane of the medium 116. The object 122 may be confined or movedby an acoustic pressure gradient directed toward the ultrasoundintensity well 118 from the surrounding region 120 of the medium 116.

In examples where the ultrasound wave 114 is transmitted by an acoustictransducer comprising one or more transducer elements (e.g., acoustictransducer 210 of FIG. 2), steering the ultrasound wave 114 so that theobject 122 is within the ultrasound intensity well 118 may includeadjusting input signals provided respectively to the one or moretransducer elements, as is known in the art. This may include situationswhere the ultrasound wave 114 is steered to move the object 122 indirections parallel to the focal plane of the medium 116.

In other examples, steering the ultrasound wave 114 so that the object122 is within the ultrasound intensity well 118 may include mechanicallyadjusting the acoustic transducer 110, as is known in the art. This mayinclude situations where the ultrasound wave 114 is steered to move theobject 122 in directions parallel to the focal plane of the medium 116.

FIG. 10 shows rotation of an object 122 via a mechanical torque 123provided by an ultrasound wave 114. The mechanical torque 123 may be aproduct of a rotational pressure gradient exhibited by the surroundingregion 120 formed by the ultrasound wave 114. For example, theprogressive phase shift imparted to the ultrasound wave 114 by eitherthe acoustic transducer 210, the acoustic lens 300, or the acoustic lens400 may generate the rotational pressure gradient and apply themechanical torque 123 to the object 122. The object 122 may vibrateand/or move about the ultrasound intensity well 118 and contact an inneredge of the surrounding region 120 from time to time, causing rotationof the object 122 via the mechanical torque 123 as shown in FIG. 10.Although in FIG. 10 rotation of the object 122 is shown in the clockwisedirection, counterclockwise rotation with respect to the focal plane ofthe medium 116 is also possible.

While various example aspects and example embodiments have beendisclosed herein, other aspects and embodiments will be apparent tothose skilled in the art. The various example aspects and exampleembodiments disclosed herein are for purposes of illustration and arenot intended to be limiting, with the true scope and spirit beingindicated by the following claims.

1. A method comprising: transmitting a focused ultrasound wave into amedium to form (i) an ultrasound intensity well within the medium thatexhibits a first range of acoustic pressure and (ii) a surroundingregion of the medium that surrounds the ultrasound intensity well andexhibits a second range of acoustic pressure that exceeds the firstrange of acoustic pressure; and confining an object within theultrasound intensity well.
 2. The method of claim 1, whereintransmitting the ultrasound wave comprises each transducer element of anarray of m transducer elements transmitting a respective component ofthe ultrasound wave that is phase shifted by 2πL/m radians with respectto a component of the ultrasound wave transmitted by an adjacenttransducer element, wherein L is a nonzero integer and m is greater thanor equal to
 3. 3. The method of claim 2, wherein m is equal to
 12. 4.The method of any of claims 2-3, wherein L is equal to −6, −5, −4, −3,−2, −1, 1, 2, 3, 4, 5, or
 6. 5. The method of claim 1, whereintransmitting the ultrasound wave into the medium comprises: transmittinga first component of the ultrasound wave through an acoustic lens at afirst azimuth angle θ=θ₁, wherein the acoustic lens imparts a firstphase shift L*θ₁ to the first component, wherein L is a nonzero integer;and transmitting a second component of the ultrasound wave through theacoustic lens at a second azimuth angle θ=θ₂, wherein the acoustic lensimparts a second phase shift L*θ₂ to the second component.
 6. The methodof claim 5, wherein the first phase shift is imparted to the firstcomponent by a first section of the acoustic lens, wherein the secondphase shift is imparted to the second component by the first section ofthe acoustic lens, and wherein transmitting the ultrasound wave into themedium further comprises: focusing the first component upon a focalplane of the medium by transmitting the first component through a secondsection of the acoustic lens, the second section comprising a curvedsurface; and focusing the second component upon the focal plane of themedium by transmitting the second component through the second sectionof the acoustic lens.
 7. The method of any of claims 5-6, wherein theacoustic lens has a varying longitudinal thickness that increasesproportionally with respect to increasing azimuth angle of the acousticlens.
 8. The method of any of claims 5-7, wherein at the first azimuthangle θ=θ₁ the acoustic lens has a first longitudinal thicknessA*L*θ₁+B, wherein A and B are nonzero positive numbers, and wherein atthe second azimuth angle θ=θ₂ the acoustic lens has a secondlongitudinal thickness A*L*θ₂+B.
 9. The method of any of claims 1-8,wherein the ultrasound wave oscillates at a frequency greater than about20 kHz and less than about 10 MHz.
 10. The method of any of claims 1-8,wherein the ultrasound wave oscillates at a frequency of about 1.5 MHz.11. The method of any of claims 1-8, wherein the ultrasound waveoscillates at a frequency of about 0.33 MHz.
 12. The method of any ofclaims 8-11, wherein${A = \frac{1}{2\; {\pi \left( {\frac{1}{\lambda_{m}} - \frac{1}{\lambda_{p}}} \right)}}},$wherein λ_(m) is a wavelength of the ultrasound wave propagating throughthe medium, and wherein λ_(p) is a wavelength of the ultrasound wavepropagating through the acoustic lens.
 13. The method of any of claims5-12, wherein L is equal to −6, −5, −4, −3, −2, −1, 1, 2, 3, 4, 5, or 6.14. The method of claim 1, wherein transmitting the ultrasound wave intothe medium comprises: transmitting a first component of the ultrasoundwave through an acoustic lens comprising p segments, wherein p isgreater than or equal to 2, wherein the first component is transmittedthrough the acoustic lens at a first azimuth angle θ=θ₃, wherein theacoustic lens imparts a first phase shift L*θ₃ to the first component,wherein L is an integer multiple of p; and transmitting a secondcomponent of the ultrasound wave through the acoustic lens at a secondazimuth angle θ=θ₄, wherein the acoustic lens imparts a second phaseshift L*θ₄ to the second component.
 15. The method of claim 14, whereinL is equal to p.
 16. The method of any of claims 14-15, wherein thefirst phase shift is imparted to the first component by a first sectionof the acoustic lens comprising the p segments, wherein the second phaseshift is imparted to the second component by the first section of theacoustic lens, and wherein transmitting the ultrasound wave into themedium further comprises: focusing the first component upon a focalplane of the medium by transmitting the first component through a secondsection of the acoustic lens, the second section comprising a curvedsurface; and focusing the second component upon the focal plane of themedium by transmitting the second component through the second sectionof the acoustic lens.
 17. The method of any of claims 14-16, whereineach of the p segments has a respective varying longitudinal thicknessthat increases proportionally with respect to increasing azimuth angleof each of the p segments.
 18. The method of any of claims 14-17,wherein the ultrasound wave oscillates at a frequency greater than about20 kHz and less than about 10 MHz.
 19. The method of any of claims14-17, wherein the ultrasound wave oscillates at a frequency of about1.5 MHz.
 20. The method of any of claims 14-17, wherein the ultrasoundwave oscillates at a frequency of about 0.33 MHz.
 21. The method of anyof claims 14-20, wherein at the first azimuth angle θ=θ₃ the acousticlens has a first longitudinal thickness C*L*θ₃+D, wherein C and D arenonzero positive numbers, and wherein at the second azimuth angle θ=θ₄the acoustic lens has a second longitudinal thickness C*L*θ₄+D.
 22. Themethod of claim 21, wherein${C = \frac{1}{2\; {\pi \left( {\frac{1}{\lambda_{m}} - \frac{1}{\lambda_{p}}} \right)}}},$wherein λ_(m) is a wavelength of the ultrasound wave propagating throughthe medium, and wherein λ_(p) is a wavelength of the ultrasound wavepropagating through the acoustic lens.
 23. The method of any of claims14-22, wherein L is equal to −6, −5, −4, −3, −2, 2, 3, 4, 5, or
 6. 24.The method of any of claims 14-23, wherein p is equal to L.
 25. Themethod of any of claims 14-23, wherein p and L are equal to
 6. 26. Themethod of any of claims 1-25, wherein confining the object within theultrasound intensity well comprises steering the ultrasound wave so thatthe object is within the ultrasound intensity well.
 27. The method ofclaim 26, wherein the ultrasound wave is transmitted by an acoustictransducer comprising one or more transducer elements, and whereinsteering the ultrasound wave so that the object is within the ultrasoundintensity well comprises adjusting input signals provided respectivelyto the one or more transducer elements.
 28. The method of claim 26,wherein the ultrasound wave is transmitted by an acoustic transducer,and wherein steering the ultrasound wave so that the object is withinthe ultrasound intensity well comprises mechanically adjusting theacoustic transducer.
 29. The method of any of claims 1-28, wherein theultrasound wave is focused at a focal plane of the medium, the methodfurther comprising: steering the ultrasound wave to move the object in adirection parallel to the focal plane by moving the ultrasound intensitywell within the focal plane.
 30. The method of claim 29, wherein theultrasound wave is transmitted by an acoustic transducer comprising oneor more transducer elements, and wherein steering the ultrasound wave tomove the object in the direction parallel to the focal plane comprisesadjusting input signals provided respectively to the one or moretransducer elements.
 31. The method of claim 29, wherein the ultrasoundwave is transmitted by an acoustic transducer, and wherein steering theultrasound wave to move the object in the direction parallel to thefocal plane comprises mechanically adjusting the acoustic transducer.32. The method of any of claims 1-31, wherein the ultrasound wave isfocused at a focal plane of the medium, and wherein the object isconfined by an acoustic pressure gradient directed toward the ultrasoundintensity well from the surrounding region of the medium.
 33. The methodof any of claims 1-32, wherein the ultrasound wave is focused at a focalplane of the medium, and wherein the surrounding region has an annularshape within the focal plane.
 34. The method of any of claims 1-33,wherein the surrounding region applies a mechanical torque to theobject.
 35. The method of claim 34, further comprising causing rotationof the object via the mechanical torque.
 36. The method of any of claims1-35, wherein the ultrasound wave is focused upon a focal point withinthe ultrasound intensity well, and wherein the focal point exhibits alocal minimum of acoustic pressure in the focal plane.
 37. The method ofany of claims 1-36, wherein the medium comprises human tissue, andwherein the object comprises a kidney stone.
 38. The method of any ofclaims 1-36, wherein the medium comprises human tissue, and wherein theobject comprises a urinary tract stone.
 39. The method of any of claims1-36, wherein the medium comprises human tissue, and wherein the objectcomprises a ureter stone.
 40. The method of any of claims 1-36, whereinthe medium comprises human tissue, and wherein the object comprises abladder stone.
 41. The method of any of claims 1-36, wherein the mediumcomprises human tissue, and wherein the object comprises a urethrastone.
 42. The method of any of claims 1-36, wherein the mediumcomprises human tissue, and wherein the object comprises a prostatestone.
 43. The method of any of claims 1-36, wherein the mediumcomprises human tissue, and wherein the object comprises a salivarystone.
 44. The method of any of claims 1-36, wherein the mediumcomprises human tissue, and wherein the object comprises a gallbladderstone.
 45. The method of any of claims 1-36, wherein the mediumcomprises human tissue, and wherein the object comprises a gall stone.46. The method of any of claims 1-36, wherein the medium comprises humantissue, and wherein the object comprises a bile duct stone.
 47. Themethod of any of claims 1-36, wherein the medium comprises human tissue,and wherein the object comprises a blood clot.
 48. The method of any ofclaims 1-36, wherein the medium comprises human tissue, and wherein theobject comprises blood.
 49. The method of any of claims 1-36, whereinthe medium comprises human tissue, and wherein the object comprisesmucous.
 50. The method of any of claims 1-36, wherein the mediumcomprises human tissue, and wherein the object comprises fecal matter.51. The method of any of claims 1-36, wherein the medium comprises humantissue, and wherein the object comprises cerumen.
 52. The method of anyof claims 1-36, wherein the medium comprises human tissue, and whereinthe object comprises a calcification.
 53. The method of any of claims1-36, wherein the medium comprises human tissue, and wherein the objectcomprises a calcified plaque.
 54. The method of any of claims 1-36,wherein the medium comprises human tissue, and wherein the objectcomprises an atherosclerotic plaque.
 55. The method of any of claims1-36, wherein the medium comprises human tissue, and wherein the objectcomprises uric acid.
 56. The method of any of claims 1-36, wherein themedium comprises human tissue, and wherein the object comprisesstruvite.
 57. The method of any of claims 1-36, wherein the mediumcomprises human tissue, and wherein the object comprises calcium oxalatemonohydrate.
 58. The method of any of claims 1-36, wherein the mediumcomprises human tissue, and wherein the object comprises cystine. 59.The method of any of claims 1-36, wherein the medium comprises humantissue, and wherein the object comprises a tonsil stone.
 60. The methodof any of claims 1-36, wherein the medium comprises human tissue, andwherein the object comprises solid non-biological matter.
 61. The methodof any of claims 1-36, wherein the medium comprises a liquid medium, andwherein the object comprises an electronic component.
 62. The method ofany of claims 1-36, wherein the medium comprises a medium on a petridish, and wherein the object comprises biological tissue.
 63. The methodof any of claims 1-36, wherein the medium comprises a liquid medium on amicroscope slide.
 64. The method of any of claims 1-63, wherein theultrasound wave is focused via an acoustic lens.
 65. The method of anyof claims 1-63, wherein the ultrasound wave is focused via an array ofcurved transducer elements that collectively transmit the ultrasoundwave.
 66. An acoustic lens configured to be acoustically coupled to anacoustic transducer, the acoustic lens having a varying longitudinalthickness that increases proportionally with respect to increasingazimuth angle of the acoustic lens.
 67. The acoustic lens of claim 66,wherein the acoustic lens has a first longitudinal thickness A*L*θ₁+B ata first azimuth angle θ=θ₁, wherein A and B are nonzero positive numbersand L is a nonzero integer, wherein the acoustic lens has a secondlongitudinal thickness A*L*θ₂+B at a second azimuth angle θ=θ₂, theacoustic lens comprising a boundary at which the varying longitudinalthickness discontinuously changes from A*L*2π+B to B.
 68. The acousticlens of claim 67, wherein L is equal to −6, −5, −4, −3, −2, −1, 1, 2, 3,4, 5, or
 6. 69. The acoustic lens of any of claims 67-68, wherein${A = \frac{\lambda_{m}}{2\; {\pi \left( {1 - n} \right)}}},$ whereinλ_(m) is greater than about 148.2 μm and less than about 74.1 mm, andwherein n is an acoustic refractive index of the acoustic lens relativeto the medium.
 70. The acoustic lens of claim 69, wherein λ_(m) is aboutequal to 988 μm.
 71. The acoustic lens of claim 69, wherein λ_(m) isabout equal to 4.49 mm.
 72. The acoustic lens of any of claims 66-71,wherein a longitudinal thickness of the acoustic lens is substantiallyconstant along a radial direction of the acoustic lens.
 73. The acousticlens of any of claims 67-72, wherein the first longitudinal thickness ofthe acoustic lens is a longitudinal thickness of a first section of theacoustic lens, wherein the second longitudinal thickness of the acousticlens is a longitudinal thickness of the first section of the acousticlens, the acoustic lens further comprising: a second section comprisinga curved surface configured to focus, upon a focal plane, components ofan ultrasound wave received at respective azimuth angles of the acousticlens.
 74. An acoustic lens configured to be acoustically coupled to anacoustic transducer, the acoustic lens comprising a plurality ofsegments, each of the plurality of segments having a varyinglongitudinal thickness that increases proportionally with respect toincreasing azimuth angle of the segment.
 75. The acoustic lens of claim74, wherein the plurality of segments comprises an array of p segments,wherein a first segment of the p segments has a first longitudinalthickness C*L*θ₃+D at a first azimuth angle θ=θ₃, wherein C and D arenonzero positive numbers and L is a nonzero integer; wherein the firstsegment has a second longitudinal thickness C*L*θ₄+D at a second azimuthangle θ=θ₄, the acoustic lens comprising a boundary between the firstsegment and a second segment of the array of p segments at which alongitudinal thickness of the acoustic lens changes from C*L*(2π/p)+D toD.
 76. The acoustic lens of claim 75, wherein L is equal to −6, −5, −4,−3, −2, 2, 3, 4, 5, or
 6. 77. The acoustic lens of any of claims 75-76,wherein L is equal to p.
 78. The acoustic lens of any of claims 75-76,wherein p and L are equal to
 6. 79. The acoustic lens of any of claims75-78, wherein${C = \frac{\lambda_{m}}{2\; {\pi \left( {1 - n} \right)}}},$ whereinλ_(m) is greater than about 148.2 μm and less than about 74.1 mm, andwherein n is an acoustic refractive index of the acoustic lens relativeto the medium.
 80. The acoustic lens of claim 79, wherein λ_(m) is aboutequal to 988 μm.
 81. The acoustic lens of claim 79, wherein λ_(m) isabout equal to 4.49 mm.
 82. The acoustic lens of any of claims 74-81,wherein a longitudinal thickness of the acoustic lens is substantiallyconstant along a radial direction of the acoustic lens.
 83. The acousticlens of any of claims 74-82, wherein the first longitudinal thickness ofthe acoustic lens is a longitudinal thickness of a first section of theacoustic lens, wherein the second longitudinal thickness of the acousticlens is a longitudinal thickness of the first section of the acousticlens, the acoustic lens further comprising: a second section comprisinga curved surface configured to focus, upon a focal plane, components ofan ultrasound wave received at respective azimuth angles of the acousticlens.
 84. The acoustic lens of any of claims 66-83, wherein the acousticlens is acoustically coupled to an acoustic transducer.
 85. A devicecomprising: an acoustic transducer; one or more processors; and acomputer-readable medium storing instructions that, when executed by theone or more processors, cause the acoustic transducer to performfunctions comprising: transmitting a focused ultrasound wave into amedium to form (i) an ultrasound intensity well within the medium thatexhibits a first range of acoustic pressure and (ii) a surroundingregion of the medium that surrounds the ultrasound intensity well andexhibits a second range of acoustic pressure that exceeds the firstrange of acoustic pressure; and confining an object within theultrasound intensity well.
 86. The device of claim 85, wherein theacoustic transducer comprises an array of m transducer elements, andwherein transmitting the ultrasound wave comprises each of the mtransducer elements transmitting a respective component of theultrasound wave that is phase shifted by 2πL/m radians with respect to acomponent of the ultrasound wave transmitted by an adjacent transducerelement, wherein L is a nonzero integer and m is greater than or equalto
 3. 87. The device of claim 86, wherein m is equal to
 12. 88. Thedevice of any of claims 86-87, wherein L is equal to −6, −5, −4, −3, −2,−1, 1, 2, 3, 4, 5, or
 6. 89. The device of claim 85, further comprisingan acoustic lens acoustically coupled to the acoustic transducer,wherein transmitting the ultrasound wave into the medium comprises:transmitting a first component of the ultrasound wave through theacoustic lens at a first azimuth angle θ=θ₁, wherein the acoustic lensimparts a first phase shift L*θ₁ to the first component, wherein L is anonzero integer; and transmitting a second component of the ultrasoundwave through the acoustic lens at a second azimuth angle θ=θ₂, whereinthe acoustic lens imparts a second phase shift L*θ₂ to the secondcomponent.
 90. The device of claim 89, wherein the acoustic lenscomprises a (i) first section and (ii) a second section comprising acurved surface, wherein the first phase shift is imparted to the firstcomponent by the first section of the acoustic lens, wherein the secondphase shift is imparted to the second component by the first section ofthe acoustic lens, and wherein transmitting the ultrasound wave into themedium further comprises: focusing the first component upon a focalplane of the medium by transmitting the first component through thesecond section of the acoustic lens; and focusing the second componentupon the focal plane of the medium by transmitting the second componentthrough the second section of the acoustic lens.
 91. The device of anyof claims 89-90, wherein the acoustic lens has a varying longitudinalthickness that increases proportionally with respect to increasingazimuth angle of the acoustic lens.
 92. The device of any of claims89-91, wherein at the first azimuth angle θ=θ₁ the acoustic lens has afirst longitudinal thickness A*L*θ₁+B, wherein A and B are nonzeropositive numbers, and wherein at the second azimuth angle θ=θ₂ theacoustic lens has a second longitudinal thickness A*L*θ₂+B.
 93. Thedevice of any of claims 85-92, wherein the ultrasound wave oscillates ata frequency greater than about 20 kHz and less than about 10 MHz. 94.The device of any of claims 85-92, wherein the ultrasound waveoscillates at a frequency of about 1.5 MHz.
 95. The device of any ofclaims 85-92, wherein the ultrasound wave oscillates at a frequency ofabout 0.33 MHz.
 96. The device of any of claims 92-95, wherein${A = \frac{\lambda_{m}}{2\; {\pi \left( {1 - n} \right)}}},$ whereinλ_(m) is greater than about 148.2 μm and less than about 74.1 mm, andwherein n is an acoustic refractive index of the acoustic lens relativeto the medium.
 97. The device of claim 96, wherein λ_(m) is about equalto 988 μm.
 98. The device of claim 96, wherein λ_(m) is about equal to4.49 mm.
 99. The device of any of claims 85-91, wherein L is equal to−6, −5, −4, −3, −2, −1, 1, 2, 3, 4, 5, or
 6. 100. The device of claim85, further comprising an acoustic lens comprising p segments, whereintransmitting the ultrasound wave into the medium comprises: transmittinga first component of the ultrasound wave through the acoustic lens,wherein p is greater than or equal to 2, wherein the first component istransmitted through the acoustic lens at a first azimuth angle θ=θ₃,wherein the acoustic lens imparts a first phase shift L*θ₃ to the firstcomponent, wherein L is an integer multiple of p; and transmitting asecond component of the ultrasound wave through the acoustic lens at asecond azimuth angle θ=θ₄, wherein the acoustic lens imparts a secondphase shift L*θ₄ to the second component.
 101. The device of claim 100,wherein L is equal to p.
 102. The device of any of claims 100-101,wherein the acoustic lens comprises a (i) first section comprising the psegments and (ii) a second section comprising a curved surface, whereinthe first phase shift is imparted to the first component by the firstsection of the acoustic lens, wherein the second phase shift is impartedto the second component by the first section of the acoustic lens, andwherein transmitting the ultrasound wave into the medium furthercomprises: focusing the first component upon a focal plane of the mediumby transmitting the first component through the second section of theacoustic lens; and focusing the second component upon the focal plane ofthe medium by transmitting the second component through the secondsection of the acoustic lens.
 103. The device of any of claims 100-102,wherein each of the p segments has a respective varying longitudinalthickness that increases proportionally with respect to increasingazimuth angle of the segment.
 104. The device of any of claims 100-103,wherein the ultrasound wave oscillates at a frequency greater than about20 kHz and less than about 10 MHz.
 105. The device of any of claims100-103, wherein the ultrasound wave oscillates at a frequency of about1.5 MHz.
 106. The device of any of claims 100-103, wherein theultrasound wave oscillates at a frequency of about 0.33 MHz.
 107. Thedevice of any of claims 100-106, wherein at the first azimuth angle θ=θ₃the acoustic lens has a first longitudinal thickness C*L*θ₃+D, wherein Cand D are nonzero positive numbers, and wherein at the second azimuthangle θ=θ₄ the acoustic lens has a second longitudinal thicknessC*L*θ₄+D.
 108. The device of claim 107, wherein${C = \frac{\lambda_{m}}{2\; {\pi \left( {1 - n} \right)}}},$ whereinλ_(m) is greater than about 148.2 μm and less than about 74.1 mm, andwherein n is an acoustic refractive index of the acoustic lens relativeto the medium.
 109. The device of claim 108, wherein λ_(m) is aboutequal to 988 μm.
 110. The device of claim 108, wherein λ_(m) is aboutequal to 4.49 mm.
 111. The device of any of claims 100-100, wherein L isequal to −6, −5, −4, −3, −2, 2, 3, 4, 5, or
 6. 112. The device of any ofclaims 100-110, wherein p is equal to L.
 113. The device of any ofclaims 100-110, wherein p and L are equal to
 6. 114. The device of anyof claims 85-113, wherein confining the object within the ultrasoundintensity well comprises steering the ultrasound wave so that the objectis within the ultrasound intensity well.
 115. The device of claim 114,wherein the acoustic transducer comprises one or more transducerelements, and wherein steering the ultrasound wave so that the object iswithin the ultrasound intensity well comprises adjusting input signalsprovided respectively to the one or more transducer elements.
 116. Thedevice of claim 114, wherein steering the ultrasound wave so that theobject is within the ultrasound intensity well comprises mechanicallyadjusting the acoustic transducer.
 117. The device of any of claims85-116, wherein the ultrasound wave is focused at a focal plane of themedium, the functions further comprising: steering the ultrasound waveto move the object in a direction parallel to the focal plane by movingthe ultrasound intensity well within the focal plane.
 118. The device ofclaim 117, wherein the acoustic transducer comprises one or moretransducer elements, and wherein steering the ultrasound wave to movethe object in the direction parallel to the focal plane comprisesadjusting input signals provided respectively to the one or moretransducer elements.
 119. The device of claim 117, wherein steering theultrasound wave to move the object in the direction parallel to thefocal plane comprises mechanically adjusting the acoustic transducer.120. The device of any of claims 85-119, wherein the ultrasound wave isfocused at a focal plane of the medium, and wherein the object isconfined by an acoustic pressure gradient directed toward the ultrasoundintensity well from the surrounding region of the medium.
 121. Thedevice of any of claims 85-120, wherein the ultrasound wave is focusedat a focal plane of the medium, and wherein the surrounding region hasan annular shape within the focal plane.
 122. The device of any ofclaims 85-120, wherein the surrounding region applies a mechanicaltorque to the object.
 123. The device of claim 122, the functionsfurther comprising causing rotation of the object via the mechanicaltorque.
 124. The device of any of claims 85-123, wherein the ultrasoundwave is focused upon a focal point within the ultrasound intensity well,and wherein the focal point exhibits a local minimum of acousticpressure.
 125. The device of any of claims 85-124, further comprising anacoustic lens, wherein the ultrasound wave is focused via the acousticlens.
 126. The device of any of claims 85-125, wherein the acoustictransducer comprises an array of curved transducer elements, and whereinthe ultrasound wave is focused via the array of curved transducerelements that collectively transmit the ultrasound wave.
 127. The deviceof any of claims 85-126, wherein the computer-readable medium is anon-transitory computer-readable medium.
 128. A computer-readablestorage medium storing instructions that, when executed by a computingdevice comprising an acoustic transducer and/or an acoustic lens, causethe acoustic transducer and/or the acoustic lens to perform the methodof any of claims 1-65.
 129. The computer-readable storage medium ofclaim 128, wherein the computer-readable storage medium is anon-transitory computer-readable storage medium.